In order to prevent mutual interference of a plurality of elements formed on a semiconductor substrate, there is conventionally known technology in which the elements adjoining each other are electrically isolated.
For example, there is known a method that includes a step of sequentially layering a silicon oxide film and a silicon nitride film on a silicon substrate and removing a portion of the silicon nitride film by etching using a photoresist as a mask, a step of selectively oxidizing a portion of the silicon oxide film exposed by the removal of the silicon nitride film to thereby form a LOCOS oxide film in the exposed portion of the silicon oxide film, and a step of forming buried oxide films on the silicon substrate at opposite sides of the LOCOS oxide film. In this method, an inter-element isolating region is made up of the LOCOS oxide film and the buried oxide films.
The above-described element isolating technology may also be used in, for example, electrically isolating an active region in which an element is formed from a marginal area defining an outer edge of a semiconductor device.